2. Carbohydrates – Structure and classification
• Carbohydrates consist of carbon, hydrogen, and oxygen.
• The general empirical structure for carbohydrates is (CH2O)n.
• They are organic compounds organized in the form of aldehydes or
ketones with multiple hydroxyl groups coming off the carbon chain.
• The carbohydrates can be structurally represented in any of the three
forms:
✔ Open chain structure.
✔ Hemi-acetal structure.
✔ Haworth structure.
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9. Monosaccharides
⮚ These are simplest of carbohydrates and are known as sugars.
⮚ These are the building units of complex carbohydrates.
⮚ These cannot be hydrolysed.
⮚ These are sweet-tasting, crystalline and soluble in water.
⮚ They have a potential aldehyde or keto group and hence, are
reducing in nature. aldose sugars.
⮚ Monosaccharide’s having keto group are known as ketoses or
ketose sugars.
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11. Oligosaccharides:
⮚ These consist of more than one but fewer number of
monosaccharide molecules joined together by glycosidic
bonds.
⮚ On hydrolysis, they yield the monosaccharide units which
may be similar or dissimilar.
⮚ These are also sweet tasting, crystalline, soluble sugars.
⮚ Disaccharides. C12H22O11 (e.g., sucrose, maltose, lactose
etc.)
⮚ Trisaccharides, C18H32O16 (e.g., raffinose, gentianose etc.)
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12. Isomers:
⮚ Two compounds having the same molecular formula but
different structural formula are known as isomers. The
number of isomers can be calculated from the number of
chiral centres (n).
Epimers:
⮚ When sugars differ only in the configuration around one
specific carbon atom they are called epimers. e.g., Glucose
and mannose are epimers at C2 whereas glucose and galactose
are epimers at C4.
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13. Polysaccharide Definition
⮚A polysaccharide is a large molecule made of many
smaller monosaccharides. Monosaccharides are
simple sugars, like glucose.
⮚ Special enzymes bind these small monomers together
creating large sugar polymers, or polysaccharides.
⮚A polysaccharide is also called a glycan.
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14. ⮚ A polysaccharide can be a homopolysaccharide, in which all the
monosaccharides are the same, or a heteropolysaccharide in which
the monosaccharides vary.
⮚ Depending on which monosaccharides are connected, and which
carbons in the monosaccharides connects, polysaccharides take on
a variety of forms.
⮚ A molecule with a straight chain of monosaccharides is called a
linear polysaccharide, while a chain that has arms and turns is
known as a branched polysaccharide.
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15. Polysaccharides(Glycans):
⮚ These are also compound sugars and yield more than 10molecules
of monosaccharide's on hydrolysis.
⮚ Polysaccharides have general formula (C6H10O5)x.
⮚ They may be linear or branched chain polysaccharides.
⮚ They may be further classified depending on whether the
monosaccharide molecules produced on hydrolysis are of same
type or of different types
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16. Homopolysaccharides:
Produce same type of monosaccharide molecules on hydrolysis.
E.g. starch(containsD-glucoseunits),glycogen (containsD- glucoseunits),
cellulose (containsD-glucoseunits), chitin (composedofN-
acetylglucosamineresidues)etc.
Heteropolysaccharides:
Produce two or more different types of monosaccharide molecules on
hydrolysis. E.g. hyaluronicacid (containsalternatingresiduesofD-
glucuronicacidandN-acetylglucosamine)
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18. Cellulose:
Cellulose occurs exclusively in plants and it is the most abundant organic substance in plant
kingdom.
⮚ It is predominant constituent of plant cell wall.
⮚ Cellulose is totally absent in animal body.
⮚ Cellulose is composed of β (1→4) glycosidic bonds.
⮚ Cellulose can not be digested by mammals- including man- due to lack of the enzyme that
cleaves β (1→4) glycosidic bonds.
⮚ Certain ruminants and herbivorous animals contain microorganisms in the gut which
produce enzymes that can cleave β (1→4) glycosidic bonds.
⮚ Hydrolysis of cellulose yields a disaccharide cellobiose followed by β-D-glucose.
⮚ It is a linear polymer.
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19. Chitin
Chitin is composed of N-acetyl D-glucosamine units held
together by β (1→4) glycosidic bonds.
It is a structural polysaccharide found in the exoskeleton of some
invertebrates e.g. insects, crustaceans.
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20. Inulin
⮚ It is a polymer of fructose i.e. fructosan.
⮚ It occurs in garlic, onion etc.
⮚ It is a low molecular weight (around 5,000)
polysaccharide easily soluble in water.
⮚ Inulin is not utilized by the body.
⮚ It is used for assessing kidney function
through measurement of glomerular
filtration rate (GFR).
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21. Heteropolysaccharides
Heteropolysaccarides contain two or more different kind of
monosaccharides.
Classified in two types
Neutral sugars, Mucopolysachharide
Neutral sugars
One type sugar units on hydrolysis
Mucopolysachharide
These are heteroglycans made up of repeating units of sugar derivatives,
namely amino sugars and uronic acids.
Mucopolysaccharides are more commonly known as glycosaminoglycans
(GAG).
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22. Mucopolysaccharides are essential components of
tissue structure.
The extracellular spaces of tissue (particularly
connective tissue-cartilage, skin, blood vessels,
tendons)
They bind proteins in the cell walls and connective
tissue.
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23. ❖keratan sulphate (acetyglucosamine + galactose +
sulphuric acid) they occur inside skin and cornea
providing both strength and flexibility.
❖ Chondroitin sulphate (glucuronic or iduronic acid
+ acetyl aminogalactose) is the mucopolysaccharide
found in the matrix of cartilage and connective
tissue for support and elasticity.
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24. Chondroitin-6-sulfate is also present in many tissues. As evident
from name, the sulfate group is found on C6 instead of C4 .
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25. ❖ Hyaluronic acid (glucuronic acid +acetyl glucosamine) is the
mucopolysaccharide met in extracellular fluid of animal
tissues, vitreous humor of eye, synovial fluid, cerebrospinal
fluid, etc.
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26. Heparin:
❖ Heparin is anticoagulant that occurs in blood, liver, lung, kidney,
spleen etc. Heparin helps in the release of the enzyme lipoprotein
lipase which causes clearing the turbidity of lipemic plasma.
❖ Heparin is composed of alternating units of N-sulfo-D-
glucosamine-6- sulfate and glucuronate-2-sulfate.
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27. ❖ Dermatan sulfate: The name dermatan sulfate is derived from
the fact that this compound mostly occurs in the skin.
❖ Agar. Marine brown and red algae, called sea weeds, yield
mucopolysaccharides commercial value, e.g., agar, alginic acid,
carragenin, etc.
❖ Agar (agar-agar) It is used as culture medium in the
laboratory, as laxative, stabilising and emulsifying agent.
❖ It is obtained from cell wall of some red alae like Gracilaria,
Gelidium and Gelidiella.
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28. ⮚ Structural components of
cell
⮚ Major source of energy
⮚ Storage substance of
potential energy
⮚ Regulation of fat
metabolism
⮚ Protein sparing function
⮚ Role in gastro intestinal
function
⮚ Key role of metabolism
⮚ Cell recognition
⮚ Supportive function
⮚ Protective function
⮚ Biological cement
⮚ Anticoagulant
Function of carbohydrate
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